Most piano teachers have favorite students. Their impression of what kind of persons their student is has a big influence on a lot of what happens during a lesson. Good teachers try as much as they can not to let their prejudices with a student show, but it's hard. At the very least, you have students whom you look forward to and students that make you think "it's seven pm already? ugh, I just want to go home."
As a student, remember that your piano teacher only sees you one or two hours each week. What he sees in those couple of hours makes up his opinion of you, and considering that his opinion has a huge influence on the dynamics of each lesson, you should make sure you are at your best during that couple of hours. If you are at your music school, also be extra careful not to fool around too much on the piano if your teacher might be around to listen. You might be a very hard-working person, and just want to let off some steam, but if the two or three times your teacher happened to listen to you practice, you were playing something completely different from what you are supposed to be working on, or just goofing around, playing extra loud or extra fast that might give him the impression that you do that all the time.
I made that mistake with one of my teachers when I was younger. During my first lessons with her, I didn't bother to dress up a bit before class, and I showed up with some ripped sneakers and patched up pants to some classes. Later, she had the unshakable conviction that I was extremely poor, and she kept offering money and to pay for my bus fare.
The impression you make around your teachers is very important, you don't want them to get the wrong idea about you into their heads.